Packaging of semiconductor x-ray detectors

ABSTRACT

Disclosed herein is an image sensor comprising: a plurality of packages arranged in a plurality of layers; wherein each of the packages comprises an X-ray detector mounted on a printed circuit board (PCB); wherein the packages are mounted on one or more system PCBs; wherein within an area encompassing a plurality of the X-ray detectors in the plurality of packages, a dead zone of the packages in each of the plurality of layers is shadowed by the packages in the other layers.

TECHNICAL FIELD

The disclosure herein relates to X-ray detectors, particularly relatesto methods of packaging semiconductor X-ray detectors.

BACKGROUND

X-ray detectors may be devices used to measure the flux, spatialdistribution, spectrum or other properties of X-rays.

X-ray detectors may be used for many applications. One importantapplication is imaging. X-ray imaging is a radiography technique and canbe used to reveal the internal structure of a non-uniformly composed andopaque object such as the human body.

Early X-ray detectors for imaging include photographic plates andphotographic films. A photographic plate may be a glass plate with acoating of light-sensitive emulsion. Although photographic plates werereplaced by photographic films, they may still be used in specialsituations due to the superior quality they offer and their extremestability. A photographic film may be a plastic film (e.g., a strip orsheet) with a coating of light-sensitive emulsion.

In the 1980s, photostimulable phosphor plates (PSP plates) becameavailable. A PSP plate may contain a phosphor material with colorcenters in its lattice. When the PSP plate is exposed to X-ray,electrons excited by X-ray are trapped in the color centers until theyare stimulated by a laser beam scanning over the plate surface. As theplate is scanned by laser, trapped excited electrons give off light,which is collected by a photomultiplier tube. The collected light isconverted into a digital image. In contrast to photographic plates andphotographic films, PSP plates can be reused.

Another kind of X-ray detectors are X-ray image intensifiers. Componentsof an X-ray image intensifier are usually sealed in a vacuum. Incontrast to photographic plates, photographic films, and PSP plates,X-ray image intensifiers may produce real-time images, i.e., do notrequire post-exposure processing to produce images. X-ray first hits aninput phosphor (e.g., cesium iodide) and is converted to visible light.The visible light then hits a photocathode (e.g., a thin metal layercontaining cesium and antimony compounds) and causes emission ofelectrons. The number of emitted electrons is proportional to theintensity of the incident X-ray. The emitted electrons are projected,through electron optics, onto an output phosphor and cause the outputphosphor to produce a visible-light image.

Scintillators operate somewhat similarly to X-ray image intensifiers inthat scintillators (e.g., sodium iodide) absorb X-ray and emit visiblelight, which can then be detected by a suitable image sensor for visiblelight. In scintillators, the visible light spreads and scatters in alldirections and thus reduces spatial resolution. Reducing thescintillator thickness helps to improve the spatial resolution but alsoreduces absorption of X-ray. A scintillator thus has to strike acompromise between absorption efficiency and resolution.

Semiconductor X-ray detectors largely overcome this problem by directconversion of X-ray into electric signals. A semiconductor X-raydetector may include a semiconductor layer that absorbs X-ray inwavelengths of interest. When an X-ray photon is absorbed in thesemiconductor layer, multiple charge carriers (e.g., electrons andholes) are generated and swept under an electric field towardselectrical contacts on the semiconductor layer. Cumbersome heatmanagement required in currently available semiconductor X-ray detectors(e.g., Medipix) can make a detector with a large area and a large numberof pixels difficult or impossible to produce.

SUMMARY

Disclosed herein is an image sensor comprising: a plurality of packagesarranged in a plurality of layers; wherein each of the packagescomprises an X-ray detector mounted on a printed circuit board (PCB);wherein the packages are mounted on one or more system PCBs; whereinwithin an area encompassing a plurality of the X-ray detectors in theplurality of packages, a dead zone of the packages in each of theplurality of layers is shadowed by the packages in the other layers.

According to an embodiment, the packages are parallel to the one or moresystem PCBs.

According to an embodiment, the packages are tilted relative to the oneor more system PCBs.

According to an embodiment, the packages in at least one of the layersare arranged in rows.

According to an embodiment, the packages in at least one of the rowspartially overlap with one another.

According to an embodiment, among the packages in that row, a part of adead zone of one package is shadowed by its neighboring package.

According to an embodiment, the packages in different layers are mountedon different system PCBs.

According to an embodiment, the packages are arranged such that lightincident in the area is detectable by at least one of the packages.

According to an embodiment, the packages are arranged such that lightincident in the area is detectable by at least two of the packages.

According to an embodiment, at least some of the packages each comprisemultiple X-ray detectors mounted on the PCB.

According to an embodiment, the X-ray detector of at least one packagecomprises a perimeter zone wherein light incident in the perimeter zoneis not detectable by the X-ray detector.

According to an embodiment, the packages are mounted on the one or moresystem PCBs by wire bonding.

According to an embodiment, the packages are rectangular in shape.

According to an embodiment, the packages are hexagonal in shape.

According to an embodiment, the packages are mounted on the one or moresystem PCBs by plugs and receptacles.

According to an embodiment, the packages are mounted on the one or moresystem PCBs by plugs, spacers and receptacles.

According to an embodiment, the X-ray detector of at least one of thepackages comprises an X-ray absorption layer and an electronics layer;wherein the X-ray absorption layer comprises an electrode; wherein theelectronics layer comprises an electronics system; wherein theelectronics system comprises: a first voltage comparator configured tocompare a voltage of the electrode to a first threshold; a secondvoltage comparator configured to compare the voltage to a secondthreshold; a counter configured to register a number of X-ray photonsreaching the X-ray absorption layer; a controller; wherein thecontroller is configured to start a time delay from a time at which thefirst voltage comparator determines that an absolute value of thevoltage equals or exceeds an absolute value of the first threshold;wherein the controller is configured to activate the second voltagecomparator during the time delay; wherein the controller is configuredto cause the number registered by the counter to increase by one, if thesecond voltage comparator determines that an absolute value of thevoltage equals or exceeds an absolute value of the second threshold.

According to an embodiment, the electronics system further comprises acapacitor module electrically connected to the electrode, wherein thecapacitor module is configured to collect charge carriers from theelectrode.

According to an embodiment, the controller is configured to activate thesecond voltage comparator at a beginning or expiration of the timedelay.

According to an embodiment, the electronics system further comprises avoltmeter, wherein the controller is configured to cause the voltmeterto measure the voltage upon expiration of the time delay.

According to an embodiment, the controller is configured to determine anX-ray photon energy based on a value of the voltage measured uponexpiration of the time delay.

According to an embodiment, the controller is configured to connect theelectrode to an electrical ground.

According to an embodiment, a rate of change of the voltage issubstantially zero at expiration of the time delay.

According to an embodiment, a rate of change of the voltage issubstantially non-zero at expiration of the time delay.

Disclosed herein is a system comprising the image sensor disclosedherein and an X-ray source, wherein the system is configured to performX-ray radiography on human chest or abdomen.

Disclosed herein is a system comprising the image sensor disclosedherein and an X-ray source, wherein the system is configured to performX-ray radiography on human mouth.

Disclosed herein is a cargo scanning or non-intrusive inspection (NII)system, comprising the image sensor disclosed herein and an X-raysource, wherein the cargo scanning or non-intrusive inspection (NII)system is configured to form an image using backscattered X-ray.

Disclosed herein is a cargo scanning or non-intrusive inspection (NII)system, comprising the image sensor disclosed herein and an X-raysource, wherein the cargo scanning or non-intrusive inspection (NII)system is configured to form an image using X-ray transmitted through anobject inspected.

Disclosed herein is a full-body scanner system comprising the imagesensor disclosed herein and an X-ray source.

Disclosed herein is an X-ray computed tomography (X-ray CT) systemcomprising the image sensor disclosed herein and an X-ray source.

Disclosed herein is an electron microscope comprising the image sensordisclosed herein, an electron source and an electronic optical system.

Disclosed herein is a system comprising the image sensor disclosedherein, wherein the system is an X-ray telescope, or an X-raymicroscopy, or wherein the system is configured to perform mammography,industrial defect detection, microradiography, casting inspection, weldinspection, or digital subtraction angiography.

BRIEF DESCRIPTION OF FIGURES

FIG. 1A schematically shows a cross-sectional view of the detector,according to an embodiment.

FIG. 1B schematically shows a detailed cross-sectional view of thedetector, according to an embodiment.

FIG. 1C schematically shows an alternative detailed cross-sectional viewof the detector, according to an embodiment.

FIG. 2 schematically shows that the device may have an array of pixels,according to an embodiment.

FIG. 3 schematically shows a cross-sectional view of an electronicslayer in the detector, according to an embodiment.

FIG. 4A schematically shows a top view of a package including one copyof the detector and a printed circuit board (PCB).

FIG. 4B schematically shows a cross-sectional view of an image sensor,where a plurality of the packages of FIG. 4A are mounted to another PCB.

FIG. 5A and FIG. 5B schematically show a multiple layer arrangement ofpackages of FIG. 4A in an image sensor, according to an embodiment.

FIG. 6A and FIG. 6B schematically show a multiple layer arrangement ofpackages of FIG. 4A in an image sensor, according to an embodiment.

FIG. 7A and FIG. 7B schematically show a multiple layer arrangement ofpackages of FIG. 4A in an image sensor, according to an embodiment.

FIG. 8A schematically shows a top view of a package including multiplecopies of the detector and a printed circuit board (PCB).

FIG. 8B schematically shows a cross-sectional view of an image sensor,where a plurality of the packages of FIG. 8A are mounted to another PCB.

FIG. 9A and FIG. 9B schematically show a multiple layer arrangement ofpackages of FIG. 8A in an image sensor, according to an embodiment.

FIG. 10A and FIG. 10B schematically show a multiple layer arrangement ofpackages of FIG. 8A in an image sensor, according to an embodiment.

FIG. 11A and FIG. 10B schematically show a multiple layer arrangement ofpackages of FIG. 8A in an image sensor, according to an embodiment.

FIG. 12A schematically shows an example of a set of four packages, eachincluding multiple detectors mounted to a single PCB.

FIG. 12B schematically shows that the four packages may be stacked in animage sensor.

FIG. 12C schematically shows a cross-sectional view of the image sensor.

FIG. 13A schematically shows an example of a set of three packages, eachincluding multiple detectors mounted to a single PCB.

FIG. 13B schematically shows that the three packages may be stacked inan image sensor.

FIG. 13C schematically shows a cross-sectional view of the image sensor.

FIG. 14A schematically shows an example of a set of three packages, eachincluding multiple detectors mounted to a single PCB.

FIG. 14B schematically shows that the three packages may be stacked inan image sensor.

FIG. 14C schematically shows a cross-sectional view of the image sensor.

FIG. 15A schematically shows how packages of FIG. 4A or FIG. 8A indifferent layers may be mounted to a PCB in an image sensor, accordingto an embodiment.

FIG. 15B schematically shows how packages of FIG. 4A or FIG. 8A indifferent layers may be mounted to a PCB in an image sensor, accordingto an embodiment.

FIG. 16 schematically shows a system comprising the semiconductor X-raydetector described herein, suitable for medical imaging such as chestX-ray radiography, abdominal X-ray radiography, etc., according to anembodiment

FIG. 17 schematically shows a system comprising the semiconductor X-raydetector described herein suitable for dental X-ray radiography,according to an embodiment.

FIG. 18 schematically shows a cargo scanning or non-intrusive inspection(NII) system comprising the semiconductor X-ray detector describedherein, according to an embodiment.

FIG. 19 schematically shows another cargo scanning or non-intrusiveinspection (NII) system comprising the semiconductor X-ray detectordescribed herein, according to an embodiment.

FIG. 20 schematically shows a full-body scanner system comprising thesemiconductor X-ray detector described herein, according to anembodiment.

FIG. 21 schematically shows an X-ray computed tomography (X-ray CT)system comprising the semiconductor X-ray detector described herein,according to an embodiment.

FIG. 22 schematically shows an electron microscope comprising thesemiconductor X-ray detector described herein, according to anembodiment.

FIG. 23A and FIG. 23B each show a component diagram of an electronicsystem of the detector in FIG. 1A or FIG. 1B, according to anembodiment.

FIG. 24 schematically shows a temporal change of the electric currentflowing through an electrode (upper curve) of a diode or an electricalcontact of a resistor of an X-ray absorption layer exposed to X-ray, theelectric current caused by charge carriers generated by an X-ray photonincident on the X-ray absorption layer, and a corresponding temporalchange of the voltage of the electrode (lower curve), according to anembodiment.

FIG. 25 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by noise (e.g., darkcurrent), and a corresponding temporal change of the voltage of theelectrode (lower curve), in the electronic system operating in the wayshown in FIG. 24, according to an embodiment.

FIG. 26 schematically shows a temporal change of the electric currentflowing through an electrode (upper curve) of the X-ray absorption layerexposed to X-ray, the electric current caused by charge carriersgenerated by an X-ray photon incident on the X-ray absorption layer, anda corresponding temporal change of the voltage of the electrode (lowercurve), when the electronic system operates to detect incident X-rayphotons at a higher rate, according to an embodiment.

FIG. 27 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by noise (e.g., darkcurrent), and a corresponding temporal change of the voltage of theelectrode (lower curve), in the electronic system operating in the wayshown in FIG. 26, according to an embodiment.

FIG. 28 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by charge carriersgenerated by a series of X-ray photons incident on the X-ray absorptionlayer, and a corresponding temporal change of the voltage of theelectrode, in the electronic system operating in the way shown in FIG.10 with RST expires before t_(e), according to an embodiment.

DETAILED DESCRIPTION

FIG. 1A schematically shows a cross-sectional view of the detector 100,according to an embodiment. The detector 100 may include an X-rayabsorption layer 110 and an electronics layer 120 (e.g., an ASIC) forprocessing or analyzing electrical signals incident X-ray generates inthe X-ray absorption layer 110. In an embodiment, the detector 100 doesnot comprise a scintillator. The X-ray absorption layer 110 may includea semiconductor material such as, silicon, germanium, GaAs, CdTe,CdZnTe, or a combination thereof. The semiconductor may have a high massattenuation coefficient for the X-ray energy of interest.

As shown in a detailed cross-sectional view of the detector 100 in FIG.1B, according to an embodiment, the X-ray absorption layer 110 mayinclude one or more diodes (e.g., p-i-n or p-n) formed by a first dopedregion 111, one or more discrete regions 114 of a second doped region113. The second doped region 113 may be separated from the first dopedregion 111 by an optional the intrinsic region 112. The discreteportions 114 are separated from one another by the first doped region111 or the intrinsic region 112. The first doped region 111 and thesecond doped region 113 have opposite types of doping (e.g., region 111is p-type and region 113 is n-type, or region 111 is n-type and region113 is p-type). In the example in FIG. 1B, each of the discrete regions114 of the second doped region 113 forms a diode with the first dopedregion 111 and the optional intrinsic region 112. Namely, in the examplein FIG. 1B, the X-ray absorption layer 110 has a plurality of diodeshaving the first doped region 111 as a shared electrode. The first dopedregion 111 may also have discrete portions.

When an X-ray photon hits the X-ray absorption layer 110 includingdiodes, the X-ray photon may be absorbed and generate one or more chargecarriers by a number of mechanisms. An X-ray photon may generate 10 to100000 charge carriers. The charge carriers may drift to the electrodesof one of the diodes under an electric field. The field may be anexternal electric field. The electrical contact 119B may includediscrete portions each of which is in electrical contact with thediscrete regions 114. In an embodiment, the charge carriers may drift indirections such that the charge carriers generated by a single X-rayphoton are not substantially shared by two different discrete regions114 (“not substantially shared” here means less than 2%, less than 0.5%,less than 0.1%, or less than 0.01% of these charge carriers flow to adifferent one of the discrete regions 114 than the rest of the chargecarriers). Charge carriers generated by an X-ray photon incident aroundthe footprint of one of these discrete regions 114 are not substantiallyshared with another of these discrete regions 114. A pixel 150associated with a discrete region 114 may be an area around the discreteregion 114 in which substantially all (more than 98%, more than 99.5%,more than 99.9%, or more than 99.99% of) charge carriers generated by anX-ray photon incident therein flow to the discrete region 114. Namely,less than 2%, less than 1%, less than 0.1%, or less than 0.01% of thesecharge carriers flow beyond the pixel.

As shown in an alternative detailed cross-sectional view of the detector100 in FIG. 1C, according to an embodiment, the X-ray absorption layer110 may include a resistor of a semiconductor material such as, silicon,germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does notinclude a diode. The semiconductor may have a high mass attenuationcoefficient for the X-ray energy of interest.

When an X-ray photon hits the X-ray absorption layer 110 including aresistor but not diodes, it may be absorbed and generate one or morecharge carriers by a number of mechanisms. An X-ray photon may generate10 to 100000 charge carriers. The charge carriers may drift to theelectrical contacts 119A and 119B under an electric field. The field maybe an external electric field. The electrical contact 119B includesdiscrete portions. In an embodiment, the charge carriers may drift indirections such that the charge carriers generated by a single X-rayphoton are not substantially shared by two different discrete portionsof the electrical contact 119B (“not substantially shared” here meansless than 2%, less than 0.5%, less than 0.1%, or less than 0.01% ofthese charge carriers flow to a different one of the discrete portionsthan the rest of the charge carriers). Charge carriers generated by anX-ray photon incident around the footprint of one of these discreteportions of the electrical contact 119B are not substantially sharedwith another of these discrete portions of the electrical contact 119B.A pixel 150 associated with a discrete portion of the electrical contact119B may be an area around the discrete portion in which substantiallyall (more than 98%, more than 99.5%, more than 99.9% or more than 99.99%of) charge carriers generated by an X-ray photon incident therein flowto the discrete portion of the electrical contact 119B. Namely, lessthan 2%, less than 0.5%, less than 0.1%, or less than 0.01% of thesecharge carriers flow beyond the pixel associated with the one discreteportion of the electrical contact 119B.

The electronics layer 120 may include an electronic system 121 suitablefor processing or interpreting signals generated by X-ray photonsincident on the X-ray absorption layer 110. The electronic system 121may include an analog circuitry such as a filter network, amplifiers,integrators, and comparators, or a digital circuitry such as amicroprocessors, and memory. The electronic system 121 may includecomponents shared by the pixels or components dedicated to a singlepixel. For example, the electronic system 121 may include an amplifierdedicated to each pixel and a microprocessor shared among all thepixels. The electronic system 121 may be electrically connected to thepixels by vias 131. Space among the vias may be filled with a fillermaterial 130, which may increase the mechanical stability of theconnection of the electronics layer 120 to the X-ray absorption layer110. Other bonding techniques are possible to connect the electronicsystem 121 to the pixels without using vias.

FIG. 2 schematically shows that the detector 100 may have an array ofpixels 150. The array may be a rectangular array, a honeycomb array, ahexagonal array or any other suitable array. Each pixel 150 may beconfigured to detect an X-ray photon incident thereon, measure theenergy of the X-ray photon, or both. For example, each pixel 150 may beconfigured to count numbers of X-ray photons incident thereon whoseenergy falls in a plurality of bins, within a period of time. All thepixels 150 may be configured to count the numbers of X-ray photonsincident thereon within a plurality of bins of energy within the sameperiod of time. Each pixel 150 may have its own analog-to-digitalconverter (ADC) configured to digitize an analog signal representing theenergy of an incident X-ray photon into a digital signal. The ADC mayhave a resolution of 10 bits or higher. Each pixel 150 may be configuredto measure its dark current, such as before or concurrently with eachX-ray photon incident thereon. Each pixel 150 may be configured todeduct the contribution of the dark current from the energy of the X-rayphoton incident thereon. The pixels 150 may be configured to operate inparallel. For example, when one pixel 150 measures an incident X-rayphoton, another pixel 150 may be waiting for an X-ray photon to arrive.The pixels 150 may be but do not have to be individually addressable.

FIG. 3 schematically shows the electronics layer 120 according to anembodiment. The electronic layer 120 comprises a substrate 122 having afirst surface 124 and a second surface 128. A “surface” as used hereinis not necessarily exposed, but can be buried wholly or partially. Theelectronic layer 120 comprises one or more electric contacts 125 on thefirst surface 124. The one or more electric contacts 125 may beconfigured to be electrically connected to one or more electricalcontacts 119B of the X-ray absorption layer 110. The electronics system121 may be in or on the substrate 122.

The substrate 122 may be a thinned substrate. For example, the substratemay have at thickness of 750 microns or less, 200 microns or less, 100microns or less, 50 microns or less, 20 microns or less, or 5 microns orless. The substrate 122 may be a silicon substrate or a substrate orother suitable semiconductor or insulator. The substrate 122 may beproduced by grinding a thicker substrate to a desired thickness.

The one or more electric contacts 125 may be a layer of metal or dopedsemiconductor. For example, the electric contacts 125 may be gold,copper, platinum, palladium, doped silicon, etc.

FIG. 3 schematically shows bonding between the X-ray absorption layer110 and the electronic layer 120 at the electrical contact 119B of theX-ray absorption layer 110 and electrical contacts 125 of the electroniclayer 120. The bonding may be by a suitable technique such as directbonding or flip chip bonding.

Direct bonding is a wafer bonding process without any additionalintermediate layers (e.g., solder bumps). The bonding process is basedon chemical bonds between two surfaces. Direct bonding may be atelevated temperature but not necessarily so.

Flip chip bonding uses solder bumps 199 deposited onto contact pads(e.g., the electrical contact 119B of the X-ray absorption layer 110 orthe electrical contacts 125). Either the X-ray absorption layer 110 orthe electronic layer 120 is flipped over and the electrical contact 119Bof the X-ray absorption layer 110 are aligned to the electrical contacts125. The solder bumps 199 may be melted to solder the electrical contact119B and the electrical contacts 125 together. Any void space among thesolder bumps 199 may be filled with an insulating material.

FIG. 4A schematically shows a top view of a package 200 including thedetector 100 and a printed circuit board (PCB) 400. The term “PCB” asused herein is not limited to a particular material. For example, a PCBmay include a semiconductor. The detector 100 is mounted to the PCB 400.The wiring between the detector 100 and the PCB 400 is not shown for thesake of clarity. The PCB 400 has only a single detector 100. The PCB 400may have an area not covered by the detector 100, for accommodatingbonding wires 410. The detector 100 may have an active area 190, whichis where the pixels 150 are located. The detector 100 may have aperimeter zone 195 near the edges of the detector 100. The perimeterzone 195 has no pixels and the detector 100 does not detect photonsincident on the perimeter zone 195.

The electrical connection between the PCBs 400 in the packages 200 and asystem PCB 450 are made by bonding wires 410. In order to accommodatethe bonding wires 410 on the PCB 400, the PCB 400 has an area 405 notcovered by the detector 100. In order to accommodate the bonding wires410 on the system PCB 450, the packages 200 have gaps in between. Thegaps may be approximately 1 mm or more. Light incident on the perimeterzones 195, on the area 405 or on the gaps cannot be detected by thepackages 200 on the system PCB 450. A dead zone of a package (e.g.,package 200) is the area of the photon-receiving surface of the package,in which incident photons cannot be detected by the detector ordetectors in the package. In this example shown in FIG. 4A, the deadzone of the package 200 includes the perimeter zones 195 and the area405. A dead zone (e.g., 488) of a group of packages (e.g., packagesmounted on the same PCB, packages arranged in the same layer) is thecombination of the dead zones of the packages in the group and the gapsamong the packages.

In order to capture the light incident in the dead zone 488 of a layerof the packages, the packages 200 may be arranged in multiple layers,where the packages 200 are arranged such that light incident on the deadzone 488 of one layer is captured by the packages 200 in another layer.

FIG. 5A and FIG. 5B schematically show a multiple layer arrangement ofpackages 200 in an image sensor, according to an embodiment. In thisembodiment, the packages 200 are arranged in at least three layers 510,520 and 530. All of the packages 200 may be mounted to a system PCB 500.The packages 200 may be parallel to the system PCB 500 as shown in thecross-sectional view in FIG. 5B. The layer 510 is closest to the systemPCB 500 among the layers 510, 520 and 530. The layer 530 is farthestfrom the system PCB 500 among the layers 510, 520 and 530. Within anarea marked by the dotted box (in a top view in FIG. 5A) and dotteddouble arrow (in a cross-sectional view in FIG. 5B), the dead zone ofthe layer 510 is shadowed by the packages 200 in the layer 520 or thepackages 200 in the layer 530; the dead zone of the layer 520 isshadowed by the packages 200 in the layer 530 or the packages 200 in thelayer 510; the dead zone of the layer 530 is shadowed by the packages200 in the layer 510 or the packages 200 in the layer 520. The term“shadowed” does not imply a particular order; a first area shadowed by asecond area means that the first area is entirely within the perimeterof the second area when viewed along a direction perpendicular to thesystem PCB, notwithstanding that the first area and the second area maybe in different layers. The area marked by the dotted box or dotteddouble arrow encompasses a plurality of the detectors 100 among those inthe three layers 510, 520 and 530. Light incident in the area marked bythe dotted box or dotted double arrow is within an active area of atleast one package 200 among those in the three layers 510, 520 and 530.Namely, light incident in the area marked by the dotted box or dotteddouble arrow is detectable by at least one package 200 among those inthe layers 510, 520 and 530. According to an embodiment, the packages200 arranged in the at least three layers 510, 520 and 530 may berespectively mounted to PCBs 511, 521 and 531; the PCBs 511, 521 and 531may be mounted to the system PCB 500.

FIG. 6A and FIG. 6B schematically show a multiple layer arrangement ofpackages 200 in an image sensor, according to an embodiment. In thisembodiment, the packages 200 are arranged in at least two layers 610 and620. The packages 200 in the layers 610 and 620 are respectively mountedto a system PCB 601 and a system PCB 602. The packages 200 may be tiltedrelative to the system PCB 601 and system PCB 602 as shown in thecross-sectional view in FIG. 6B. The packages 200 within the layer 610or the layer 620 are arranged in rows. The packages 200 in a rowpartially overlap with one another (analogous to a column of roofingshingles) as shown in FIG. 6A and FIG. 6B, such that, within a row, apart of the dead zone of a package is shadowed by its neighboringpackage. Within an area marked by the dotted box (in a top view in FIG.6A) and dotted double arrow (in a cross-sectional view in FIG. 6B), thedead zone (including the gaps between the rows) of the layer 610 isshadowed by the rows of packages 200 in the layer 620; the dead zone ofthe layer 620 is shadowed by the rows of packages 200 in the layer 610.The area marked by the dotted box or dotted double arrow encompasses aplurality of the detectors 100 among those in the two layers 610 and620. Light incident in the area marked by the dotted box or dotteddouble arrow is within an active area of at least one package 200 amongthose in the layers 610 and 620. Namely, light incident in the areamarked by the dotted box or dotted double arrow is detectable by atleast one package 200 among those in the layers 610 and 620.

FIG. 7A and FIG. 7B schematically show a multiple layer arrangement ofpackages 200 in an image sensor, according to an embodiment. Thisembodiment is similar to that illustrated in FIG. 6A and FIG. 6B exceptthat the packages 200 are arranged in at least three layers 710, 720 and730. The packages 200 in the layers 710, 720 and 730 are respectivelymounted to a system PCB 701, a system PCB 702 and a system PCB 703. Thepackages 200 may be tilted relative to the system PCB 701, 702 or 703 asshown in the cross-sectional view in FIG. 7B. The packages 200 withineach of the layers 710, 720 and 730 are arranged in rows. The packages200 in a row partially overlap with one another (analogous to a columnof roofing shingles) as shown in FIG. 7A and FIG. 7B, such that, withina row, a part of the dead zone of a package is shadowed by itsneighboring package. Within an area marked by the dotted box (in a topview in FIG. 7A) and dotted double arrow (in a cross-sectional view inFIG. 7B), the dead zone (including the gaps between the rows) of thelayer 710 is shadowed by the rows of packages 200 in both of the layers720 and 730; the dead zone of the layer 720 is shadowed by the rows ofpackages 200 in both of the layers 710 and 730; the dead zone of thelayer 730 is shadowed by the rows of packages 200 in both of the layers710 and 720. The area marked by the dotted box or dotted double arrowencompasses a plurality of the detectors 100 among those in the threelayers 710, 720 and 730. Light incident in the area marked by the dottedbox or dotted double arrow is within an active area of at least twopackages 200 among those in the layers 710, 720 and 730. Namely, lightincident in the area marked by the dotted box or dotted double arrow isdetectable by at least two packages 200 among those in the layers 710,720 and 730.

Unlike the package 200 illustrated in FIG. 4A, multiple detectors 100may be mounted onto a PCB. FIG. 8A schematically shows a packageincluding multiple detectors 100 mounted to a single PCB 899. The PCB899 may have an area 805 not covered by the detector 100. The area 805may include a portion of the PCB 810 for accommodating bonding wires 810and gaps between the multiple detectors 100. Each of the detectors 100has an active area 190, which is where the pixels 150 are located. Eachof the detectors 100 may have a perimeter zone 195 near the edges. Theperimeter zones 195 have no pixels and the detectors 100 do not detectphotons incident on the perimeter zones 195.

FIG. 8B schematically shows a cross-sectional view of an image sensor,where a plurality of the packages 800 are mounted to a system PCB 850.The electrical connection between the PCBs 899 in the packages 800 andthe system PCB 850 are made by bonding wires 810. In order toaccommodate the bonding wires 810 on the system PCB 850, the packages800 have gaps in between. The gaps may be approximately 1 mm or more.Light incident on the areas 805 of the packages 800 or on the gapsbetween the packages 800 cannot be detected by the packages 800 on thesystem PCB 850. The dead zone 888 of the packages on the system PCB 850includes the gaps between the packages 800, the areas 805 of thepackages 800, and any perimeter zones of the detectors 100 in thepackages.

In order to capture the light incident in the dead zone 800, thepackages 800 may be arranged in multiple layers, where the packages 800are arranged such that light incident on the dead zone 888 of one layerreaches the active areas 190 of the packages 800 in another layer. Thepackage 800 than the individual detector 100. If any of the detectors100 in a package 800 malfunctions, the entire package 800 may bereplaced relatively easily because the relatively large size of thepackage 800 makes it easier to handle the package 800.

FIG. 9A and FIG. 9B schematically show a multiple layer arrangement ofpackages 800 in an image sensor, according to an embodiment. In thisembodiment, the packages 800 are arranged in at least three layers 910,920 and 930. All of the packages 800 may be mounted to a system PCB 900.The packages 800 may be parallel to the system PCB 900 as shown in thecross-sectional view in FIG. 9B. The layer 910 is closest to the systemPCB 900 among the layers 910, 920 and 930. The layer 930 is farthestfrom the system PCB 900 among the layers 910, 920 and 930. Within anarea marked by the dotted box (in a top view in FIG. 9A) and dotteddouble arrow (in a cross-sectional view in FIG. 9B), the dead zone ofthe layer 910 is shadowed by the packages 800 in the layer 920 or thepackages 800 in the layer 930; the dead zone of the layer 920 isshadowed by the packages 800 in the layer 930 or the packages 800 in thelayer 910; the dead zone of the layer 930 is shadowed by the packages800 in the layer 910 or the packages 800 in the layer 920. The areamarked by the dotted box or dotted double arrow encompasses a pluralityof the detectors 100 among those in the three layers 910, 920 and 930.Light incident in the area marked by the dotted box or dotted doublearrow is within an active area of at least one package 800 among thosein the three layers 910, 920 and 930. Namely, light incident in the areamarked by the dotted box or dotted double arrow is detectable by atleast one package 800 among those in the layers 910, 920 and 930.According to an embodiment, the packages 900 arranged in the at leastthree layers 910, 920 and 930 may be respectively mounted to PCBs 911,921 and 931; the PCBs 911, 921 and 931 may be mounted to the system PCB900.

FIG. 10A and FIG. 10B schematically show a multiple layer arrangement ofpackages 800 in an image sensor, according to an embodiment. In thisembodiment, the packages 800 are arranged in at least two layers 1010and 1020. The packages 800 in the layers 1010 and 1020 may be mounted toa system PCB 1000. The packages 800 may be tilted relative to the systemPCB 1000 as shown in the cross-sectional view in FIG. 10B. The packages800 within the layer 1010 or the layer 1020 partially overlap with oneanother (analogous to a column of roofing shingles) as shown in FIG. 10Aand FIG. 10B, such that a part of the dead zone of a package is shadowedby its neighboring package. Within an area marked by the dotted box (ina top view in FIG. 10A) and dotted double arrow (in a cross-sectionalview in FIG. 10B), the dead zone of the layer 1010 is shadowed by thepackages 800 in the layer 1020; the dead zone of the layer 1020 isshadowed by the packages 800 in the layer 1010. The area marked by thedotted box or dotted double arrow encompasses a plurality of thedetectors 100 among those in the two layers 1010 and 1020. Lightincident in the area marked by the dotted box or dotted double arrow iswithin an active area of at least one package 800 among those in thelayers 1010 and 1020. Namely, light incident in the area marked by thedotted box or dotted double arrow is detectable by at least one package800 among those in the layers 1010 and 1020. According to an embodiment,the packages 800 arranged in the at least two layers 1010 and 1020 maybe respectively mounted to PCBs 1011 and 1021; the PCBs 1011 and 1021may be mounted to the system PCB 1000.

FIG. 11A and FIG. 11B schematically show a multiple layer arrangement ofpackages 800 in an image sensor, according to an embodiment. Thisembodiment is similar to that illustrated in FIG. 10A and FIG. 10Bexcept that the packages 800 are arranged in at least three layers 1110,1120 and 1130. The packages 800 in the layers 1110, 1120 and 1130 may bemounted to a system PCB 1100. The packages 800 may be tilted relative tothe system PCB 1100 as shown in the cross-sectional view in FIG. 11B.The packages 800 within the layers 1110, 1120 or 1130 partially overlapwith one another (analogous to a column of roofing shingles) as shown inFIG. 11A and FIG. 11B, such that a part of the dead zone of a package isshadowed by its neighboring package. Within an area marked by the dottedbox (in a top view in FIG. 11A) and dotted double arrow (in across-sectional view in FIG. 11B), the dead zone of the layer 1110 isshadowed by the packages 800 in both of the layers 1120 and 1130; thedead zone of the layer 1120 is shadowed by the packages 800 in both ofthe layers 1110 and 1130; the dead zone of the layer 1130 is shadowed bythe packages 800 in both of the layers 1110 and 1120. The area marked bythe dotted box or dotted double arrow encompasses a plurality of thedetectors 100 among those in the three layers 1110, 1120 and 1130. Lightincident in the area marked by the dotted box or dotted double arrow iswithin an active area of at least two packages 800 among those in thelayers 1110, 1120 and 1130. Namely, light incident in the area marked bythe dotted box or dotted double arrow is detectable by at least twopackages 800 among those in the layers 1110, 1120 and 1130. According toan embodiment, the packages 800 arranged in the at least three layers1110, 1120 and 1130 may be respectively mounted to PCBs 1111, 1121 and1131; the PCBs 1111, 1121 and 1131 may be mounted to the system PCB1100.

FIG. 12A schematically shows an example of a set of four packages, eachincluding multiple detectors 100 mounted to a single PCB. The fourpackages each have an array of the detectors 100. The detectors 100 inthe array may be arranged in multiple columns. FIG. 12B schematicallyshows that the four packages may be stacked in an image sensor such thatlight incident in the area marked by the dotted box (in a top view inFIG. 12B) or dotted double arrow (in a cross-sectional view in FIG. 12C)is within an active area of at least two of the four packages. The areamarked by the dotted box or dotted double arrow encompasses a pluralityof the detectors 100 among those in the four packages. Namely, lightincident in the area marked by the dotted box or dotted double arrow isdetectable by at least two of the four packages.

FIG. 13A schematically shows an example of a set of three packages, eachincluding multiple detectors 100 mounted to a single PCB. The threepackages each have an array of the detectors 100. The detectors 100 inthe array may be arranged in multiple columns. FIG. 13B schematicallyshows that the three packages may be stacked in an image sensor suchthat light incident in the area marked by the dotted box (in a top viewin FIG. 13B) or dotted double arrow (in a cross-sectional view in FIG.13C) is within an active area of at least one of the three packages. Thearea marked by the dotted box or dotted double arrow encompasses aplurality of the detectors 100 among those in the three packages.Namely, light incident in the area marked by the dotted box or dotteddouble arrow is detectable by at least one of the three packages.

FIG. 14A schematically shows an example of a set of three packages, eachincluding multiple detectors 100 mounted to a single PCB. The detectors100 do not have to rectangular in shape. For example, the detectors maybe hexagonal in shape. The three packages each have an array of thedetectors 100. The detectors 100 in the array may be arranged in atriangular grid. FIG. 14B schematically shows that the three packagesmay be stacked in an image sensor such that light incident in the areamarked by the dotted box (in a top view in FIG. 14B) or dotted doublearrow (in a cross-sectional view in FIG. 14C) is within an active areaof at least one of the three packages. The area marked by the dotted boxor dotted double arrow encompasses a plurality of the detectors 100among those in the three packages. Namely, light incident in the areamarked by the dotted box or dotted double arrow is detectable by atleast one of the three packages.

FIG. 15A schematically shows how packages 200 or 800 in different layersmay be mounted to a system PCB 1500 in an image sensor, according to anembodiment. Each of the packages may have a plug 1510 electrically andmechanically connected thereto. The plugs 1510 may have differentheights for the packages in different layers. The system PCB 1500 mayhave a plurality of receptacles 1520. The packages 200 or 800 may beplugged into the receptacles 1520 and supported to different distancesfrom the system PCB 1500 by the plugs 1510.

FIG. 15B schematically shows how packages 200 or 800 in different layersmay be mounted to a system PCB 1500 in an image sensor, according to anembodiment. Each of the packages may have a plug 1510 electrically andmechanically connected thereto. The plugs 1510 have the same height forthe packages in different layers. The system PCB 1500 may have aplurality of receptacles 1520. The packages 200 or 800 may be pluggedinto spacers 1530 and the spacers 1530 may be plugged into thereceptacles 1520. The spacers 1530 may have different heights for thepackages in different layers. The packages are supported to differentdistances from the system PCB 1500 by the plugs 1510 and the spacers1530.

FIG. 16 schematically shows a system comprising an image sensor 9000 asdescribed in relation to FIG. 4A-FIG. 15B. The system may be used formedical imaging such as chest X-ray radiography, abdominal X-rayradiography, etc. The system comprises an X-ray source 1201. X-rayemitted from the X-ray source 1201 penetrates an object 1202 (e.g., ahuman body part such as chest, limb, abdomen), is attenuated bydifferent degrees by the internal structures of the object 1202 (e.g.,bones, muscle, fat and organs, etc.), and is projected to the imagesensor 9000. The image sensor 9000 forms an image by detecting theintensity distribution of the X-ray.

FIG. 17 schematically shows a system comprising an image sensor 9000 asdescribed in relation to FIG. 4A-FIG. 15B. The system may be used formedical imaging such as dental X-ray radiography. The system comprisesan X-ray source 1301. X-ray emitted from the X-ray source 1301penetrates an object 1302 that is part of a mammal (e.g., human) mouth.The object 1302 may include a maxilla bone, a palate bone, a tooth, themandible, or the tongue. The X-ray is attenuated by different degrees bythe different structures of the object 1302 and is projected to theimage sensor 9000. The image sensor 9000 forms an image by detecting theintensity distribution of the X-ray. Teeth absorb X-ray more than dentalcaries, infections, periodontal ligament. The dosage of X-ray radiationreceived by a dental patient is typically small (around 0.150 mSv for afull mouth series).

FIG. 18 schematically shows a cargo scanning or non-intrusive inspection(NII) system comprising an image sensor 9000 as described in relation toFIG. 4A-FIG. 15B. The system may be used for inspecting and identifyinggoods in transportation systems such as shipping containers, vehicles,ships, luggage, etc. The system comprises an X-ray source 1401. X-rayemitted from the X-ray source 1401 may backscatter from an object 1402(e.g., shipping containers, vehicles, ships, etc.) and be projected tothe image sensor 9000. Different internal structures of the object 1402may backscatter X-ray differently. The image sensor 9000 forms an imageby detecting the intensity distribution of the backscattered X-rayand/or energies of the backscattered X-ray photons.

FIG. 19 schematically shows another cargo scanning or non-intrusiveinspection (NII) system comprising an image sensor 9000 as described inrelation to FIG. 4A-FIG. 15B. The system may be used for luggagescreening at public transportation stations and airports. The systemcomprises an X-ray source 1501. X-ray emitted from the X-ray source 1501may penetrate a piece of luggage 1502, be differently attenuated by thecontents of the luggage, and projected to the image sensor 9000. Theimage sensor 9000 forms an image by detecting the intensity distributionof the transmitted X-ray. The system may reveal contents of luggage andidentify items forbidden on public transportation, such as firearms,narcotics, edged weapons, flammables.

FIG. 20 schematically shows a full-body scanner system comprising animage sensor 9000 as described in relation to FIG. 4A-FIG. 15B. Thefull-body scanner system may detect objects on a person's body forsecurity screening purposes, without physically removing clothes ormaking physical contact. The full-body scanner system may be able todetect non-metal objects. The full-body scanner system comprises anX-ray source 1601. X-ray emitted from the X-ray source 1601 maybackscatter from a human 1602 being screened and objects thereon, and beprojected to the image sensor 9000. The objects and the human body maybackscatter X-ray differently. The image sensor 9000 forms an image bydetecting the intensity distribution of the backscattered X-ray. Theimage sensor 9000 and the X-ray source 1601 may be configured to scanthe human in a linear or rotational direction.

FIG. 21 schematically shows an X-ray computed tomography (X-ray CT)system. The X-ray CT system uses computer-processed X-rays to producetomographic images (virtual “slices”) of specific areas of a scannedobject. The tomographic images may be used for diagnostic andtherapeutic purposes in various medical disciplines, or for flawdetection, failure analysis, metrology, assembly analysis and reverseengineering. The X-ray CT system comprises an image sensor 9000 asdescribed in relation to FIG. 4A-FIG. 15B and an X-ray source 1701. Theimage sensor 9000 and the X-ray source 1701 may be configured to rotatesynchronously along one or more circular or spiral paths.

FIG. 22 schematically shows an electron microscope. The electronmicroscope comprises an electron source 1801 (also called an electrongun) that is configured to emit electrons. The electron source 1801 mayhave various emission mechanisms such as thermionic, photocathode, coldemission, or plasmas source. The emitted electrons pass through anelectronic optical system 1803, which may be configured to shape,accelerate, or focus the electrons. The electrons then reach a sample1802 and an image detector may form an image therefrom. The electronmicroscope may comprise an image sensor 9000 as described in relation toFIG. 4A-FIG. 15B, for performing energy-dispersive X-ray spectroscopy(EDS). EDS is an analytical technique used for the elemental analysis orchemical characterization of a sample. When the electrons incident on asample, they cause emission of characteristic X-rays from the sample.The incident electrons may excite an electron in an inner shell of anatom in the sample, ejecting it from the shell while creating anelectron hole where the electron was. An electron from an outer,higher-energy shell then fills the hole, and the difference in energybetween the higher-energy shell and the lower energy shell may bereleased in the form of an X-ray. The number and energy of the X-raysemitted from the sample can be measured by the image sensor 9000.

The image sensor 9000 described here may have other applications such asin an X-ray telescope, X-ray mammography, industrial X-ray defectdetection, X-ray microscopy or microradiography, X-ray castinginspection, X-ray non-destructive testing, X-ray weld inspection, X-raydigital subtraction angiography, etc. It may be suitable to use thisimage sensor 9000 in place of a photographic plate, a photographic film,a PSP plate, an X-ray image intensifier, a scintillator, or anothersemiconductor X-ray detector.

FIG. 23A and FIG. 23B each show a component diagram of the electronicsystem 121, according to an embodiment. The electronic system 121 mayinclude a first voltage comparator 301, a second voltage comparator 302,a counter 320, a switch 305, a voltmeter 306 and a controller 310.

The first voltage comparator 301 is configured to compare the voltage ofan electrode of a diode 300 to a first threshold. The diode may be adiode formed by the first doped region 111, one of the discrete regions114 of the second doped region 113, and the optional intrinsic region112. Alternatively, the first voltage comparator 301 is configured tocompare the voltage of an electrical contact (e.g., a discrete portionof electrical contact 119B) to a first threshold. The first voltagecomparator 301 may be configured to monitor the voltage directly, orcalculate the voltage by integrating an electric current flowing throughthe diode or electrical contact over a period of time. The first voltagecomparator 301 may be controllably activated or deactivated by thecontroller 310. The first voltage comparator 301 may be a continuouscomparator. Namely, the first voltage comparator 301 may be configuredto be activated continuously, and monitor the voltage continuously. Thefirst voltage comparator 301 configured as a continuous comparatorreduces the chance that the system 121 misses signals generated by anincident X-ray photon. The first voltage comparator 301 configured as acontinuous comparator is especially suitable when the incident X-rayintensity is relatively high. The first voltage comparator 301 may be aclocked comparator, which has the benefit of lower power consumption.The first voltage comparator 301 configured as a clocked comparator maycause the system 121 to miss signals generated by some incident X-rayphotons. When the incident X-ray intensity is low, the chance of missingan incident X-ray photon is low because the time interval between twosuccessive photons is relatively long. Therefore, the first voltagecomparator 301 configured as a clocked comparator is especially suitablewhen the incident X-ray intensity is relatively low. The first thresholdmay be 5-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltageone incident X-ray photon may generate in the diode or the resistor. Themaximum voltage may depend on the energy of the incident X-ray photon(i.e., the wavelength of the incident X-ray), the material of the X-rayabsorption layer 110, and other factors. For example, the firstthreshold may be 50 mV, 100 mV, 150 mV, or 200 mV.

The second voltage comparator 302 is configured to compare the voltageto a second threshold. The second voltage comparator 302 may beconfigured to monitor the voltage directly, or calculate the voltage byintegrating an electric current flowing through the diode or theelectrical contact over a period of time. The second voltage comparator302 may be a continuous comparator. The second voltage comparator 302may be controllably activate or deactivated by the controller 310. Whenthe second voltage comparator 302 is deactivated, the power consumptionof the second voltage comparator 302 may be less than 1%, less than 5%,less than 10% or less than 20% of the power consumption when the secondvoltage comparator 302 is activated. The absolute value of the secondthreshold is greater than the absolute value of the first threshold. Asused herein, the term “absolute value” or “modulus” |x| of a real numberx is the non-negative value of x without regard to its sign. Namely,

${x} = \left\{ {\begin{matrix}{x,{{{if}\mspace{14mu} x} \geq 0}} \\{{- x},{{{if}\mspace{14mu} x} \leq 0}}\end{matrix}.} \right.$

The second threshold may be 200%-300% of the first threshold. The secondthreshold may be at least 50% of the maximum voltage one incident X-rayphoton may generate in the diode or resistor. For example, the secondthreshold may be 100 mV, 150 mV, 200 mV, 250 mV or 300 mV. The secondvoltage comparator 302 and the first voltage comparator 310 may be thesame component. Namely, the system 121 may have one voltage comparatorthat can compare a voltage with two different thresholds at differenttimes.

The first voltage comparator 301 or the second voltage comparator 302may include one or more op-amps or any other suitable circuitry. Thefirst voltage comparator 301 or the second voltage comparator 302 mayhave a high speed to allow the system 121 to operate under a high fluxof incident X-ray. However, having a high speed is often at the cost ofpower consumption.

The counter 320 is configured to register a number of X-ray photonsreaching the diode or resistor. The counter 320 may be a softwarecomponent (e.g., a number stored in a computer memory) or a hardwarecomponent (e.g., a 4017 IC and a 7490 IC).

The controller 310 may be a hardware component such as a microcontrollerand a microprocessor. The controller 310 is configured to start a timedelay from a time at which the first voltage comparator 301 determinesthat the absolute value of the voltage equals or exceeds the absolutevalue of the first threshold (e.g., the absolute value of the voltageincreases from below the absolute value of the first threshold to avalue equal to or above the absolute value of the first threshold). Theabsolute value is used here because the voltage may be negative orpositive, depending on whether the voltage of the cathode or the anodeof the diode or which electrical contact is used. The controller 310 maybe configured to keep deactivated the second voltage comparator 302, thecounter 320 and any other circuits the operation of the first voltagecomparator 301 does not require, before the time at which the firstvoltage comparator 301 determines that the absolute value of the voltageequals or exceeds the absolute value of the first threshold. The timedelay may expire before or after the voltage becomes stable, i.e., therate of change of the voltage is substantially zero. The phase “the rateof change of the voltage is substantially zero” means that temporalchange of the voltage is less than 0.1%/ns. The phase “the rate ofchange of the voltage is substantially non-zero” means that temporalchange of the voltage is at least 0.1%/ns.

The controller 310 may be configured to activate the second voltagecomparator during (including the beginning and the expiration) the timedelay. In an embodiment, the controller 310 is configured to activatethe second voltage comparator at the beginning of the time delay. Theterm “activate” means causing the component to enter an operationalstate (e.g., by sending a signal such as a voltage pulse or a logiclevel, by providing power, etc.). The term “deactivate” means causingthe component to enter a non-operational state (e.g., by sending asignal such as a voltage pulse or a logic level, by cut off power,etc.). The operational state may have higher power consumption (e.g., 10times higher, 100 times higher, 1000 times higher) than thenon-operational state. The controller 310 itself may be deactivateduntil the output of the first voltage comparator 301 activates thecontroller 310 when the absolute value of the voltage equals or exceedsthe absolute value of the first threshold.

The controller 310 may be configured to cause the number registered bythe counter 320 to increase by one, if, during the time delay, thesecond voltage comparator 302 determines that the absolute value of thevoltage equals or exceeds the absolute value of the second threshold.

The controller 310 may be configured to cause the voltmeter 306 tomeasure the voltage upon expiration of the time delay. The controller310 may be configured to connect the electrode to an electrical ground,so as to reset the voltage and discharge any charge carriers accumulatedon the electrode. In an embodiment, the electrode is connected to anelectrical ground after the expiration of the time delay. In anembodiment, the electrode is connected to an electrical ground for afinite reset time period. The controller 310 may connect the electrodeto the electrical ground by controlling the switch 305. The switch maybe a transistor such as a field-effect transistor (FET).

In an embodiment, the system 121 has no analog filter network (e.g., aRC network). In an embodiment, the system 121 has no analog circuitry.

The voltmeter 306 may feed the voltage it measures to the controller 310as an analog or digital signal.

The system 121 may include a capacitor module 309 electrically connectedto the electrode of the diode 300 or which electrical contact, whereinthe capacitor module is configured to collect charge carriers from theelectrode. The capacitor module can include a capacitor in the feedbackpath of an amplifier. The amplifier configured as such is called acapacitive transimpedance amplifier (CTIA). CTIA has high dynamic rangeby keeping the amplifier from saturating and improves thesignal-to-noise ratio by limiting the bandwidth in the signal path.Charge carriers from the electrode accumulate on the capacitor over aperiod of time (“integration period”) (e.g., as shown in FIG. 24,between t₀ to t₁, or t₁-t₂). After the integration period has expired,the capacitor voltage is sampled and then reset by a reset switch. Thecapacitor module can include a capacitor directly connected to theelectrode.

FIG. 24 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by charge carriersgenerated by an X-ray photon incident on the diode or the resistor, anda corresponding temporal change of the voltage of the electrode (lowercurve). The voltage may be an integral of the electric current withrespect to time. At time to, the X-ray photon hits the diode or theresistor, charge carriers start being generated in the diode or theresistor, electric current starts to flow through the electrode of thediode or the resistor, and the absolute value of the voltage of theelectrode or electrical contact starts to increase. At time t₁, thefirst voltage comparator 301 determines that the absolute value of thevoltage equals or exceeds the absolute value of the first threshold V1,and the controller 310 starts the time delay TD1 and the controller 310may deactivate the first voltage comparator 301 at the beginning of TD1.If the controller 310 is deactivated before t₁, the controller 310 isactivated at t₁. During TD1, the controller 310 activates the secondvoltage comparator 302. The term “during” a time delay as used heremeans the beginning and the expiration (i.e., the end) and any time inbetween. For example, the controller 310 may activate the second voltagecomparator 302 at the expiration of TD1. If during TD1, the secondvoltage comparator 302 determines that the absolute value of the voltageequals or exceeds the absolute value of the second threshold at time t₂,the controller 310 causes the number registered by the counter 320 toincrease by one. At time t_(e), all charge carriers generated by theX-ray photon drift out of the X-ray absorption layer 110. At time t_(s),the time delay TD1 expires. In the example of FIG. 24, time t_(s) isafter time t_(e); namely TD1 expires after all charge carriers generatedby the X-ray photon drift out of the X-ray absorption layer 110. Therate of change of the voltage is thus substantially zero at t_(s). Thecontroller 310 may be configured to deactivate the second voltagecomparator 302 at expiration of TD1 or at t₂, or any time in between.

The controller 310 may be configured to cause the voltmeter 306 tomeasure the voltage upon expiration of the time delay TD1. In anembodiment, the controller 310 causes the voltmeter 306 to measure thevoltage after the rate of change of the voltage becomes substantiallyzero after the expiration of the time delay TD1. The voltage at thismoment is proportional to the amount of charge carriers generated by anX-ray photon, which relates to the energy of the X-ray photon. Thecontroller 310 may be configured to determine the energy of the X-rayphoton based on voltage the voltmeter 306 measures. One way to determinethe energy is by binning the voltage. The counter 320 may have asub-counter for each bin. When the controller 310 determines that theenergy of the X-ray photon falls in a bin, the controller 310 may causethe number registered in the sub-counter for that bin to increase byone. Therefore, the system 121 may be able to detect an X-ray image andmay be able to resolve X-ray photon energies of each X-ray photon.

After TD1 expires, the controller 310 connects the electrode to anelectric ground for a reset period RST to allow charge carriersaccumulated on the electrode to flow to the ground and reset thevoltage. After RST, the system 121 is ready to detect another incidentX-ray photon. Implicitly, the rate of incident X-ray photons the system121 can handle in the example of FIG. 24 is limited by 1/(TD1+RST). Ifthe first voltage comparator 301 has been deactivated, the controller310 can activate it at any time before RST expires. If the controller310 has been deactivated, it may be activated before RST expires.

FIG. 25 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by noise (e.g., darkcurrent, background radiation, scattered X-rays, fluorescent X-rays,shared charges from adjacent pixels), and a corresponding temporalchange of the voltage of the electrode (lower curve), in the system 121operating in the way shown in FIG. 24. At time to, the noise begins. Ifthe noise is not large enough to cause the absolute value of the voltageto exceed the absolute value of V1, the controller 310 does not activatethe second voltage comparator 302. If the noise is large enough to causethe absolute value of the voltage to exceed the absolute value of V1 attime t₁ as determined by the first voltage comparator 301, thecontroller 310 starts the time delay TD1 and the controller 310 maydeactivate the first voltage comparator 301 at the beginning of TD1.During TD1 (e.g., at expiration of TD1), the controller 310 activatesthe second voltage comparator 302. The noise is very unlikely largeenough to cause the absolute value of the voltage to exceed the absolutevalue of V2 during TD1. Therefore, the controller 310 does not cause thenumber registered by the counter 320 to increase. At time t_(e), thenoise ends. At time t_(s), the time delay TD1 expires. The controller310 may be configured to deactivate the second voltage comparator 302 atexpiration of TD1. The controller 310 may be configured not to cause thevoltmeter 306 to measure the voltage if the absolute value of thevoltage does not exceed the absolute value of V2 during TD1. After TD1expires, the controller 310 connects the electrode to an electric groundfor a reset period RST to allow charge carriers accumulated on theelectrode as a result of the noise to flow to the ground and reset thevoltage. Therefore, the system 121 may be very effective in noiserejection.

FIG. 26 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by charge carriersgenerated by an X-ray photon incident on the diode or the resistor, anda corresponding temporal change of the voltage of the electrode (lowercurve), when the system 121 operates to detect incident X-ray photons ata rate higher than 1/(TD1+RST). The voltage may be an integral of theelectric current with respect to time. At time to, the X-ray photon hitsthe diode or the resistor, charge carriers start being generated in thediode or the resistor, electric current starts to flow through theelectrode of the diode or the electrical contact of resistor, and theabsolute value of the voltage of the electrode or the electrical contactstarts to increase. At time t₁, the first voltage comparator 301determines that the absolute value of the voltage equals or exceeds theabsolute value of the first threshold V1, and the controller 310 startsa time delay TD2 shorter than TD1, and the controller 310 may deactivatethe first voltage comparator 301 at the beginning of TD2. If thecontroller 310 is deactivated before t₁, the controller 310 is activatedat t₁. During TD2 (e.g., at expiration of TD2), the controller 310activates the second voltage comparator 302. If during TD2, the secondvoltage comparator 302 determines that the absolute value of the voltageequals or exceeds the absolute value of the second threshold at time t₂,the controller 310 causes the number registered by the counter 320 toincrease by one. At time t_(e), all charge carriers generated by theX-ray photon drift out of the X-ray absorption layer 110. At time t_(h),the time delay TD2 expires. In the example of FIG. 26, time t_(h) isbefore time t_(e); namely TD2 expires before all charge carriersgenerated by the X-ray photon drift out of the X-ray absorption layer110. The rate of change of the voltage is thus substantially non-zero att_(h). The controller 310 may be configured to deactivate the secondvoltage comparator 302 at expiration of TD2 or at t₂, or any time inbetween.

The controller 310 may be configured to extrapolate the voltage at t_(e)from the voltage as a function of time during TD2 and use theextrapolated voltage to determine the energy of the X-ray photon.

After TD2 expires, the controller 310 connects the electrode to anelectric ground for a reset period RST to allow charge carriersaccumulated on the electrode to flow to the ground and reset thevoltage. In an embodiment, RST expires before t_(e). The rate of changeof the voltage after RST may be substantially non-zero because allcharge carriers generated by the X-ray photon have not drifted out ofthe X-ray absorption layer 110 upon expiration of RST before t_(e). Therate of change of the voltage becomes substantially zero after t_(e) andthe voltage stabilized to a residue voltage VR after t_(e). In anembodiment, RST expires at or after t_(e), and the rate of change of thevoltage after RST may be substantially zero because all charge carriersgenerated by the X-ray photon drift out of the X-ray absorption layer110 at t_(e). After RST, the system 121 is ready to detect anotherincident X-ray photon. If the first voltage comparator 301 has beendeactivated, the controller 310 can activate it at any time before RSTexpires. If the controller 310 has been deactivated, it may be activatedbefore RST expires.

FIG. 27 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by noise (e.g., darkcurrent, background radiation, scattered X-rays, fluorescent X-rays,shared charges from adjacent pixels), and a corresponding temporalchange of the voltage of the electrode (lower curve), in the system 121operating in the way shown in FIG. 26. At time t₀, the noise begins. Ifthe noise is not large enough to cause the absolute value of the voltageto exceed the absolute value of V1, the controller 310 does not activatethe second voltage comparator 302. If the noise is large enough to causethe absolute value of the voltage to exceed the absolute value of V1 attime t₁ as determined by the first voltage comparator 301, thecontroller 310 starts the time delay TD2 and the controller 310 maydeactivate the first voltage comparator 301 at the beginning of TD2.During TD2 (e.g., at expiration of TD2), the controller 310 activatesthe second voltage comparator 302. The noise is very unlikely largeenough to cause the absolute value of the voltage to exceed the absolutevalue of V2 during TD2. Therefore, the controller 310 does not cause thenumber registered by the counter 320 to increase. At time t_(e), thenoise ends. At time t_(h), the time delay TD2 expires. The controller310 may be configured to deactivate the second voltage comparator 302 atexpiration of TD2. After TD2 expires, the controller 310 connects theelectrode to an electric ground for a reset period RST to allow chargecarriers accumulated on the electrode as a result of the noise to flowto the ground and reset the voltage. Therefore, the system 121 may bevery effective in noise rejection.

FIG. 28 schematically shows a temporal change of the electric currentflowing through the electrode (upper curve) caused by charge carriersgenerated by a series of X-ray photons incident on the diode or theresistor, and a corresponding temporal change of the voltage of theelectrode (lower curve), in the system 121 operating in the way shown inFIG. 26 with RST expires before t_(e). The voltage curve caused bycharge carriers generated by each incident X-ray photon is offset by theresidue voltage before that photon. The absolute value of the residuevoltage successively increases with each incident photon. When theabsolute value of the residue voltage exceeds V1 (see the dottedrectangle in FIG. 28), the controller starts the time delay TD2 and thecontroller 310 may deactivate the first voltage comparator 301 at thebeginning of TD2. If no other X-ray photon incidence on the diode or theresistor during TD2, the controller connects the electrode to theelectrical ground during the reset time period RST at the end of TD2,thereby resetting the residue voltage. The residue voltage thus does notcause an increase of the number registered by the counter 320.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. An image sensor comprising: a plurality ofpackages arranged in a plurality of layers; wherein each of the packagescomprises an X-ray detector mounted on a printed circuit board (PCB);wherein the packages are mounted on one or more system PCBs; whereinwithin an area encompassing a plurality of the X-ray detectors in theplurality of packages, a dead zone of the packages in each of theplurality of layers is shadowed by the packages in the other layers;wherein the packages in at least one of the layers are arranged in rows;wherein the packages in at least one of the rows partially overlap withone another.
 2. The image sensor of claim 1, wherein the packages areparallel to the one or more system PCBs.
 3. The image sensor of claim 1,wherein the packages are tilted relative to the one or more system PCBs.4. The image sensor of claim 1, wherein among the packages in that row,a part of a dead zone of one package is shadowed by its neighboringpackage.
 5. The image sensor of claim 1, wherein the packages indifferent layers are mounted on different system PCBs.
 6. The imagesensor of claim 1, wherein the packages are arranged such that lightincident in the area is detectable by at least one of the packages. 7.The image sensor of claim 1, wherein the packages are arranged such thatlight incident in the area is detectable by at least two of thepackages.
 8. The image sensor of claim 1, wherein at least some of thepackages each comprise multiple X-ray detectors mounted on the PCB. 9.The image sensor of claim 1, wherein the X-ray detector of at least onepackage comprises a perimeter zone wherein light incident in theperimeter zone is not detectable by the X-ray detector.
 10. The imagesensor of claim 1, wherein the packages are mounted on the one or moresystem PCBs by wire bonding.
 11. The image sensor of claim 1, whereinthe packages are rectangular in shape.
 12. The image sensor of claim 1,wherein the packages are hexagonal in shape.
 13. The image sensor ofclaim 1, wherein the packages are mounted on the one or more system PCBsby plugs and receptacles.
 14. The image sensor of claim 1, wherein thepackages are mounted on the one or more system PCBs by plugs, spacersand receptacles.
 15. The image sensor of claim 1, wherein the X-raydetector of at least one of the packages comprises an X-ray absorptionlayer and an electronics layer; wherein the X-ray absorption layercomprises an electrode; wherein the electronics layer comprises anelectronics system; wherein the electronics system comprises: a firstvoltage comparator configured to compare a voltage of the electrode to afirst threshold; a second voltage comparator configured to compare thevoltage to a second threshold; a counter configured to register a numberof X-ray photons reaching the X-ray absorption layer; a controller;wherein the controller is configured to start a time delay from a timeat which the first voltage comparator determines that an absolute valueof the voltage equals or exceeds an absolute value of the firstthreshold; wherein the controller is configured to activate the secondvoltage comparator during the time delay; wherein the controller isconfigured to cause the number registered by the counter to increase byone, if the second voltage comparator determines that an absolute valueof the voltage equals or exceeds an absolute value of the secondthreshold.
 16. The image sensor of claim 15, wherein the electronicssystem further comprises a capacitor module electrically connected tothe electrode, wherein the capacitor module is configured to collectcharge carriers from the electrode.
 17. The image sensor of claim 15,wherein the controller is configured to activate the second voltagecomparator at a beginning or expiration of the time delay.
 18. The imagesensor of claim 15, wherein the electronics system further comprises avoltmeter, wherein the controller is configured to cause the voltmeterto measure the voltage upon expiration of the time delay.
 19. The imagesensor of claim 15, wherein the controller is configured to determine anX-ray photon energy based on a value of the voltage measured uponexpiration of the time delay.
 20. The image sensor of claim 15, whereinthe controller is configured to connect the electrode to an electricalground.
 21. The image sensor of claim 15, wherein a rate of change ofthe voltage is substantially zero at expiration of the time delay. 22.The image sensor of claim 15, wherein a rate of change of the voltage issubstantially non-zero at expiration of the time delay.
 23. A systemcomprising the image sensor of claim 1 and an X-ray source.